This invention relates to crew masks to be used in large aircraft for crew safety and in the event of decompression of the cabin. More particularly, the invention relates to the inflatable harness used to secure such a mask in place for use.
A commonly used type of crew mask includes an inflatable head harness with inflatable elastic tubes that are inflated prior to placement of the harness over the head of the user, and that are then deflated to grip the user's head. A valve is connected to the tubes to control inflation by pressurized gas, such as from an oxygen supply of a regulator on the respiratory mask, and deflation.
Another similar type of oxygen supply system includes an oxygen supply with a face mask and an inflatable head harness. A plurality of chemical oxygen generators provide oxygen to a reservoir, to initially inflate the pneumatic head harness and provide an initial breathing supply during the startup of the chemical oxygen generators.
The prior art uses a harness, with an inflatable silicone inner tube, along with a regulator to provide oxygen for pilots. The inflation feature of the harness allows pilots to don the crew mask in a quick manner.
In a typical conventional crew mask, illustrated in FIG. 1, an inflatable crew mask assembly includes an inflatable harness 10 connected to an oronasal face seal molding or mask portion 12 formed to fit to a face of a wearer when the inflatable harness is fitted over the wearer's head and properly inflated. A lower forward portion of the mask portion includes a smoke goggle purge flow actuation lever 14, a harness inflation control button 16, a connector 18 between the inflatable harness and an oxygen supply regulator assembly 20, and a control knob 22. The regulator typically supplies breathing oxygen to the mask wearer through ports internal to the lower forward portion of the face seal, and also supplies oxygen or other breathing gas mixtures to the inflatable harness via an oxygen pressure supply hose 24, including a pressure indicator 26, coupling 28, and microphone connection cable 30. The inflatable harness typically includes a rear inflatable tube 32 or strap connected via connectors 34 to a lower inflatable tube 36 connected to the oxygen supply regulator assembly. The inflatable harness may also be adjustable for the size and comfort of the mask once inflated. Upon depression of the harness inflation button the oxygen from its source flows into the harness assembly.
The prior art relied on a silicone inner tube that inflated by pressurized oxygen and was constrained to not burst by a porous over-braid. Specifically, the prior art inflatable harness typically consists of an inflatable silicone tube treated with talc or talcum powder and covered with a braided sleeve of Nomex® braided material. The braiding helps the tube withstand higher pressures, and depending on the ratio of length of the Nomex® braided sleeve to tube length, the length of expansion can be controlled in the longitudinal direction while the diameter of the Nomex® braided sleeve controls tube expansion in the radial direction. The nominal operating pressure is 70 to 85 psig.
As seen in FIG. 1, there are several sections within the harness assembly with varying length of tubing and associated joints where these sections meet and are held in place with various means. The ends of the Nomex® covered silicone tubes are connected to the mask by means of crimped ferrules. Accessories, such as a back pad and head straps are attached to the Nomex® covered silicone tubes to create the harness shape. The ends of the braid are also taped during assembly of the harness to prevent the ends from unraveling.
During cycling of the harness assembly, the silicone tubes inflate as oxygen from the crew mask is supplied to the harness assembly, creating an increase in pressure. As noted above, the tubing increases in length in the longitudinal direction, while the radial increase in tube diameter is controlled by the Nomex® sleeve.
However, the silicone inner tube is highly susceptible to puncture and abrasion. One of the main observed failure modes of the prior art is leakage within the harness due to tears in the tube caused by stress and fatigue after repeated inflation cycles. Deformation of the tubing when a harness assembly is subjected to repeated inflation cycles causes the formation of small holes in the tubing that can consequently result in significant leakage from the tubing.
Moreover, the prior art fails to provide a robust assembly in controlling the radial diameter of the silicone tube by the Nomex® sleeve. Pleating of the Nomex® braid in manufacturing is both difficult and inconsistent. Once the harness assembly is inflated several times, the Nomex® braid pleats will form an irregular pattern along the length of the tube. This irregularity in pleat spacing creates a non-uniform radial increase in the tube diameter. This non-uniform radial increase in diameter creates areas in the tube length where the diameter will balloon. In these areas, the outer surface of the tube is eroded away, causing a decrease in tube wall thickness and eventual tube failure.
In addition, once a prior art harness has been cycled for approximately 20,000 cycles, the silicone tubing takes a set in the longitudinal direction. This set increases the length of the harness in the non-inflated condition, which has a detrimental effect on the harness tension and ultimately the ability of the crew mask to provide an adequate face seal.
It therefore would be desirable to provide an inflatable harness crew mask with an inflatable harness that is able to inflate and expand over a user's head without requiring the silicone tube to be treated with talc or talcum powder, the braid to be pleated, nor the ends of the braid to be taped during assembly of the harness. It would also be desirable to provide an inflatable harness crew mask with an inflatable harness having a braid material that is allowed to stretch in the longitudinal direction without an appreciable change in axial diameter. It would further be desirable to provide an inflatable harness crew mask with an inflatable harness having a braid whose diameter remains relatively constant over the stretched length such that the braid provides a consistent, controlled and limited expansion of the silicone tube in the radial direction. It also would be desirable to provide an inflatable harness crew mask whose number of harness cycles can be increased by 50 fold compared to the prior art, and can be inflatable from at least 18,250 times to up to 40,000 times without failure. It would be further desirable to provide an inflatable harness crew mask which has no appreciable change in harness tension measured before cycling compared to that measured after cycling. It would also be desirable to provide an inflatable harness crew mask which has significantly higher reliability than the prior art to withstand inflation related wear and tear over the lifetime of the crew mask without adding weight to the existing design. The present invention meets these and other needs.